8: 1971 GMC Sprint SP
Although the El Camino is the most well-known GM car/truck hybrid, there was also a GMC version. The GMC Sprint SP is a rarer and fairly unknown corporate clone of the El Camino. This rarity has kept the resale value of the Sprint justifiable. The 7.4-liter V-8 was a powerful engine that can still be upgraded today (via Midwest Dream Car).
The fact that the Sprint is a GMC is unique, as there has never been a GMC car. With the right amount of work, the Sprint can be a unique muscle car. The shared platform with the Chevy Chevelle means there are plenty of aftermarket parts. When it comes to uniqueness and rarity, the GMC Sprint is one of the rarest cars on the road.